Resistor material and method of making same



Patented June 10, 1930 UNITED, STATES PATENT OFFICE JOSEPH BLEPIAN, 0F SWIS SV'ALE, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC 6'5 MANUFACTURING A CORPORATION OF PENNSYLVANIA RESISTOR MATERIAL METHOD OF MAKING SAME This invention relates to resistor materials, and is directed to a method of treating materials containing an oxidizable conducting substance in order to control the resistivity thereof. More particularly, my invention relates to the treatment of bodies of relatively high resistance material to increase the resistivity thereof to any desired degree for various applications, such as for resistor plates for the disk pile type of lightning arrester.

The present application is a division and a continuation in part of my copending application, Serial No. 557 ,364, filed April 29, 1922, for resistance plates.

In the above-identified application, I have described the treatment of resistor material, generally in the form of plates, whereby there is incorporated in the plates an oxidizing material which is capable of acting on the carbonaceous ingredient thereof to oxidize the same and thus to increase the resistance of the body. Specifically, I have provided plates or other bodies of a mixture of lampblack, carborundum and kaolin, which is molded to the desired form and then fired to harden th body.

The plates are then placed in a solution of a suita le oxidizing agent, such as chromic acid in water, after which they are dried. The chromic acid does not act on the material at ordinary temperatures to any appreciable degree but, in service, if a discharge through the lightning arrester should accidently cause overheating of any portion thereof, the chromic acid at the high temperature acts upon the carbonaceous material, oxidizing it to the gaseous form and thereby raising the resistance of that portion of the plate which was unduly heated. This is particularly advantageous in that after the lightning discharge has passed, there is no tendency for power current to follow the path of the lightning discharge.

The present invention relates to the process of impregnating the plate material to produce the result. above set forth and also to a further development of the process whereby new and useful results are obtained.

It is, therefore, an object of the present invention to provide a method of treating bodies of resistor material whereby the resistivity thereof may be increased and Where- No Drawing. Original application filed April 29, 1922, Serial No. 557,364. Divided and this application flledoctober 15, 1923. Serial No. 668,552.

by the degree of increase of resistivity may be closely controlled. I

In the disk-pile lightning arrester, it is desirable that all the platesor disks thereof have uniformly high resistivity in order that the discharge characteristics of the lightning arrester may be the same at all points. In the manufacture of the lightning arrester disks, it is impossible to control the resistivity thereof as closely as is desirable and a considerable proportion of the disks have too low a resistance. Hitherto, it has been customary to raise the resistance of those disks having a low resistivity by heating the same to a red heat in the presence of air or oxygen to burn out some of the lampblack. However, the resulting disks were'not uniform in resistivity, areas of low resistance occurring at intervals along with areas having high resistance. The surfaces of the disks so treated had a higher resistivity than the interior thereof.

The present invention eliminates the disadvantages inherent in the process previously employed in that it results in a moreuniforin increase of the resistivity of the disks. In practising my invention, I provide a solution of a suitable oxidizing agent, preferably one which leaves a relatively non-conducting residue, such as chromic acid, potassium nitrate, ammonium nitrate, potassium permanganate, barium nitrate or the like. The disks are immersed in a solution oftlie oxidizing agent, such as chromic acid, for a sufiicient length of time untilthey have absorbed either a desired amount of solution or until they have become saturated. They are placed in an oven and raised to a suitable temperature, about 300 (1., sufficiently high that oxidation of the carbonaceous material will proceed. This temperature should preferably be below that at which air will act on the material.

The oxidizing process may be continued until all of the oxidizing agent has been utilized to raise the resistance of the material, or the heating may be continued for a sufficient length of time to raise the resistance of the material to the desired degree. Prefer- 1 ably, I add only suflicient oxidizing agent cation above referred to.

In accordance with my invention, I may, instead of immersing the material completely in a solution of the oxidizing agent, impregnate only certain portions thereof with the oxidizing solution, inorder to raise the resistance of any desired part thereof. For instance, my method may be used to increase the resistance of the ribs of the disk or plate structure described in my copending application, Serial No. 536,910, filed February 16, 1922, patented Sept. 23, 1924, No. 1,509,494, for disk structure. To accomplish this, I allow a solution of the oxidizing material to flow upon the rib or projection and simultaneously heat the disk to a suitable temperature to oxidize the carbonaceous material in the rib. If desired, I may first impregnate the rib with the oxidizin solution and then bake in an oven as descri ed above.

It will be noted from the description of my invention that I have provided a method of increasing the resistance of resistor material whereby any desired increase of resistivity thereof may be obtained in an extremely simple manner. The apparatus necessary to accomplish the result is very simple, consisting essentially only of a treating bath and a drying oven. It does not require a skilled operator to treat the material, since all that is necessary for him to do is to immerse the material in the oxidizing solution either until it is saturated or for a predetermined'length of time, and then place the same in the oven until the oxidizing action has been completed or for a predetermined length of time, as desired.

I claim as my invention:

1. A method of increasing the resistance of a molded composite resistor material containing an impalpably finely divided oxidizable conducting substance which comprises incorporating within the mass thereof a solid, finely divided material which is inactive under normal conditions but which is capable of exerting an oxidizing action on said conducting substance at elevated temperatures and heating said resistor material to oxidize at least some of said conducting substance.

2. A method of increasing the resistance of a molded composite resistor material con- 'tainin taining an impalpably finely divided oxidizable conductingl substance which comprises incorporating t erein a material which is inactive under normal conditions but which is capable of exerting an oxidizing action on said conducting substance at elevated temperatures and heating said resistor material to a temperature below that at which air acts thereon to oxidize at least some of said conducting substance.

3. A method of increasing the resistance of a molded composite resistor material cona finely divided oxidizable conducting su stance which comprises incorporating therein a finely divided solid material which is inactive under normal conditions but which is capable of exerting an oxidizing action on said conducting substance at elevated temperatures and which leaves a relatively nonconducting residue, and heating said resistor. material to oxidize at least some of said conducting substance.

4. A method of increasing the resistance of a molded composite resistor material containing an impalpably finely divided oxidizable conducting substance which comprises incorporating within the mass thereof a solid, finely divided inorganic oxidizing agent which is inactive under normal conditions but which is capable of exerting an oxidizing action on said conducting substance at elevated temperaturesand heating said resistor material to oxidize at least some of said conducting substance.

5. A method of increasing the resistance of a molded composite resistor material containing a finely divided oxidizable conducting substance which comprises incorporating therein an inorganic oxidizing agent which is inactive under normal conditions but which is capable of exerting an oxidizing action on said conducting substance at elevated temperatures and which leaves a non-conducting oxide residue, and heating said resistor material to oxidize at least some of said conducting substance.

6. A method of increasing the resistance of a molded composite resistor material containing a finely divided oxidizable conducting substance which comprises incorporating therein a solution of an inorganic oxidizing agent which is inactive under normal conditions but which is capable of exerting an oxidizing action on said conducting substance at elevated temperatures and heating said resistor material to oxidize at least some of said conducting substance.

7. A method of increasing the resistance of a molded composite resistor material containing an oxidizable conducting substance which comprises incorporating therein chromic acid which is inactive undernormal conditions but which is capable of exerting an oxidizing action on said conducting substance at elevated temperatures and heating said re- 8. A method of increasing the resistance "of a molded composite resistor material containing an impalpably finely divided oxidizable 5 conductin substance which comprises immersing t e resistor material in a solution of a material which is inactive under normal conditions but which is capable of exerting an oxidizing action on said conducting'substance at elevated temperatures and heating said resistor material to oxidize at least some of said conducting substance.

9. The method of increasing the resistivity of composite resistor bodies normally operating at temperatures slightly higher than the ambient atmospheric temperature, including oxidizable conducting substances which are oxidizable in air only at a significantly higher temperature than said normal operating temperatures, said method comprising subjecting some of the conducting subtsances in said bodies to a reagent other than air capable of oxidizing the same to form a gaseous oxide at temperatures higher than the normal operating temperature but below the temperature at which air oxidizes said substances, and controllably elevating the temperature of said body before putting it into normal operation to adjust the resistivity thereof to a desired value. 1

10. The method of increasing the resistivity of molded carbonaceous resistor bodies which comprises impregnating the molded bodies with an oxidizing agent that is substantially of no effect at normal operating temperatures but is of material efl'ect at temperatures between 100 C. and 500 C. and subsequently subjectin some of the carbonaceous material of sai bodies toa temperature at which said oxidizing agent reacts thereon. v

11. The method of increasing the resistivity of carbonaceous resistor bodies which comprises impregnating the same with a solution of chromic acid and subsequently heating said bodies to a temperature below 500 C. but sufliciently high to cause the chromic acid to oxidize the carbonaceous material and significantly increase the resistivities of the bodies.

12. The methodof treating molded carbonaceous resistor bodies so that the resistivity thereof will be increased in the event that they are subsequently heated to a suitable tempera- 55 to harden the same and subsequently impregor partially decomposing, said reagent.

ture, which comprises impregnating the same with a solution of chromic acid which permeates substantially through the max of said molded bodies. g

13. The method of making a composite (mv high-resistance material which comprises mixin a finely divided oxidizable conductor material with a binding and filling material capable of hardening upon treatment at an elevated temperature, sotreating the mixture nating the-same with an oxidizing agent which is decomposable at a temperature lower than that required in the previous heat treatment of said binding and filling material.

14. The method of making a composite, high-resistance material which comprises mixing a finely divided oxidizable'conductor material with a binding and filling material capable of hardening upon treatment at an elevated temperature, so treating the mixture to harden the same, subsequently impregnating the same with an oxidizing a out which is decomposable at a temperature ower than that required in the previous treatment of said binding and filling material, and subsequently heating said impregnated material to a temperature suitable for decomposing said temperature lower than that required in the previous heat treatment of said binding and filling material and subsequently heating said impregnated material to a temperature suit- ,able for decomposing said oxidizing agent.

16 The method of making a composite, high-resistance material which comprises mixing a finely divided conductor material 'with a binding and filling material capable of hardening upon treatment at an elevated temperature, so treating the mixture to harden the same, and subsequently impregnating the same with a reagent whichis decomposable, or partially decomposable, at a 4 temperature lower than that required in the previous heat treatment of said binding and lling material and is capable of reacting with said conductor material.

17. The method of making a composite,

high-resistance material which comprises mixing a finely divided conductor material with a binding and filling material capable a of hardening upon treatment at an elevated temperature, "so treating the mixture to harden the same, subsequently impregnating the same with a reagent which is decomposable, or partially decomposable, at a temperature lower than that required in the previous heat treatment of said binding and filling material and is-capable of reacting with said conductor material, and subse l quently heating said impregnated material to a temperature suitable for decomposing,

18. The process of manufacturing quantities of composite resistor bodies having a substantially uniform high resistivity, which comprises forming quantities of bodies by mixing a finely divided conductor material with a binding and filling material capable of hardening upon treatment at an elevated temperature and so treating the mixtures to harden the same, testing the resulting bodies for resistivity and treating certain bodies 1 having abnormal resistivity by subsequently impregnating the same with a reagent which is decomposable, or partially decomposable, at a temperature lower than that required in the previous heat treatment of said binding and filling material and is' capable of reacting with said conductor material and subsequently heating said impregnated material to a temperature suitable for decomposing, or partially decomposing, said reagent.

19. The method of increasing the resistivity of composite, molded, fired ceramic resistor bodies including a conducting substance which comprises impregnating said composite, molded, fired ceramic resistor bodies with a substance which permeates substantially through the mass of said molded bodies and which will react chemically with said conducting substance to form a gas at elevated temperatures less than the temperature at which said conducting substance is oxidized by air. q

20. The method of making a composite, high-resistance material out of a binding and filling material, a finely divided soluble impregnating oxidizing material and a finely divided conductor material of a nature adapted to be acted upon by said oxidizing material at temperatures above normal operating temperatures, said binding and filling material being of a nature requiring heat treatment at an elevated temperature, and said oxidizing material being substantially inoperative at normal operating temperatures but being decomposable at a temperature lower than that required in the aforesaid heat treatment of said binding and filling material, said method comprising the steps of mixing the binding and filling material and the conductor material, molding and firing the same, and subsequently impregnating said fired product with the oxidizing material.

In testimony whereof, I have hereunto subscribed my name this 9th day of October,

JOSEPH SLEPIAN. 

